1. Field of the Invention
The present invention relates to a high voltage light emitting diode (HV LED) chip and its manufacturing method. In particular, the present invention relates to an HV LED chip with trenches that have a high aspect ratio and its manufacturing method, wherein each of the trenches has a width of about 0.5 μm to about 7 μm.
2. Descriptions of the Related Art
The light emitting diode (LED) is a “green lighting source” because it is both power-saving and eco-friendly. The LED has gradually replaced traditional lighting devices because of its advantages, such as a long service life, high brightness, rapid response time and small size. LED chips that were developed earlier were direct current light emitting diode (DC LED) chips, which merely comprise one LED unit and needs to be used in combination with conversion equipment such as an external transformer and rectifier. The DC LED chip not only leads to a higher energy conversion cost, but also increases the power conversion and circuit consumption. Moreover, during packaging, the volume of the circuit product and the cost for assembly, wire bonding or the like are also increased. Such a DC LED chip also has a restricted luminous efficiency and design flexibility due to its operating voltage, size limitation, current crowding phenomenon and etc., and thus, cannot completely replace traditional lighting devices.
Another LED chip is an alternating current light emitting diode (AC LED) chip, which has a plurality of LED units formed on one chip and is constructed into a circuit loop or a Wheatstone bridge to be directly used in an alternating current field. However, the AC LED chip cannot well perform the luminous efficiency of every LED unit due to such a circuit layout, and thus, has a drawback of unstable luminescence.
With the continuous research and modification in the industry, a high voltage light emitting diode (HV LED) chip has been developed recently. The HV LED chip is free of a current conversion driving component essential to the DC LED chip for light emitting, and thereby, the space can be effectively utilized. Moreover, the HV LED has a lengthened service life and enhanced design flexibility, and can prevent unstable luminescence encountered in an AC LED chip. To be compatible with existing machines, the process for manufacturing an HV LED chip is mostly based on the manufacturing currently used for AC LED chips. The process for manufacturing an HV LED chip mainly involves forming trenches in a semiconductor layer and forming an insulating layer to cover the trenches, so that the LED units (i.e., small unit grains for constituting an HV LED chip) can be isolated from each other. The existing process usually adopts an inductively coupled plasma (ICP) dry etching method to etch through a semiconductor layer to an underlying substrate to from trenches. Finally, the LED units are electrically connected by the desired circuit design.
In the above existing process, although the dry etching method can etch through the semiconductor layer and form trenches for isolation, the formed trenches are usually too broad in width. FIG. 1 is a scanning electron microscope (SEM) image of a trench fabricated using the dry etching method, wherein the trench has a width of about 15.5 μm. Such a wide trench means that a certain proportion of the light emitting area is sacrificed, and thus, the light emitting area of the LED unit is decreased and the luminous efficiency is accordingly reduced. Meanwhile, the design flexibility and minimization development of the HV LED chip are confined. Moreover, the dry etching method needs to be used in combination with the lithography process, resulting in a more complicated process. The laminating procedures are also complex and the production cost is thus increased.
In view of the above, the present invention provides a new method for manufacturing an HV LED chip. The new method does not have the disadvantages of the dry etching method and can form trenches with a relatively narrow width to increase the economical benefit of the HV LED chip.